Self heat sealable packaging and a method for making same

ABSTRACT

The present invention is directed to saturants for fibrous webs that will confer upon those webs the ability to be heat sealed to many materials without compromising the drapability of the fibrous webs. The present invention is further directed to fibrous webs saturated with the saturant of the present invention and methods for saturating such webs. The invention is further directed to packages or containers comprising the saturated webs and methods of manufacturing such packages. The invention is further directed to temperature sensitive adhesive coatings that can be used with the saturated webs and a method for applying the coating.

CLAIM OF PRIORITY

[0001] Priority is claimed to provisional Patent Application No.60/249,120, filed Nov. 16, 2000 and to provisional Patent ApplicationNo. 60/240,184, filed Oct. 13, 2000.

TECHNICAL FIELD

[0002] The present invention is directed to saturants for fibrous webs.The present invention is further directed to saturated fibrous webs andmethods for saturating such webs. The invention is further directed topackages or containers comprising the saturated webs and methods ofmanufacturing such packages. Such packages have particular utility forthe medical field, including packaging for medical instruments and otherdevices that require sterilization. The invention is further directed tocoatings used with the saturated webs, a method for applying thecoatings. The invention is further directed to fibrous webs coated withsuch coatings and articles comprising such webs.

BACKGROUND OF THE INVENTION

[0003] Many products, especially devices and supplies used in surgicaland other medical applications, must be sterilized prior to use.Examples of such products in the medical context include but are notlimited to surgical devices, implants, tubing, valves, gauzing,syringes, and protective clothing such as surgical gowns and gloves.Such products and supplies are often packaged prior to being sterilized.One sterilization procedure for such products involves using sterilizinggases that will penetrate pores in the packaging. Steam and ethyleneoxide are examples of such sterilizing gases. The gas flows through thepores in the packaging material and sterilizes the instruments containedtherein. Over time, the gas will then diffuse out of the package. Thepackaging serves to protect the instruments during sterilization and topreserve their sterility upon subsequent storage until the packages areopened for use of the product. To allow proper sterilization, packagingfor medical products should be sufficiently permeable to sterilizationgases to allow the gases to sterilize the product within. To avoidcontamination after sterilization, the packaging should also prevent theentry of bacteria and pathogens into the package.

[0004] Packaging for many medical and sterile supplies includes twocomponents, referred to herein as the base component and the breathablecover. The two components are attached to one another to form suchstructures as a pouch, which combines two flexible layers, or a rigidcontainer, which uses a rigid base component often in the form of a tubor tray with the breathable cover acting as a lid. The sterile devicesare stored between the two layers in a pouch or within the tub, tray, orother space within the rigid base component in a rigid container. Thepackage is completed by sealing the two layers together, often byheating the materials so that a seal is formed using a temperaturesensitive adhesive. When the device contained in the package is needed,the package is opened. Such packages are opened commonly and desirablyby pulling the two components apart along the seal. Examples of suchpackages are widely known and include: U.S. Pat. No. 3,991,881 toAugurt, U.S. Pat. No. 4,183,431 to Schmidt et al.; U.S. Pat. No.5,217,772 to Brown et al.; and U.S. Pat. No. 5,418,022 to Anderson etal.

[0005] Seals between components of a package must have sufficientstrength to assure that stresses resulting from package handling afterassembly will not cause the seal to open before the desired time andwill remain impervious to pathogens. Seal strength is commonly expressedas the force required to separate the two sealed layers when holding thelayers at facing edges and pulling the layers in opposite directions,commonly referred to as a “T-peel” because peeling results in the twoseparated portions of the layers forming the arms of the letter “T” withthe base of the letter “T” being the portion of the two layers thatremain attached until pulled apart. One method used to evaluate sealstrength using a “T-peel” is found in American Society of Testing andMaterials (ASTM) method F904-98. Other methods for testing seal strengthexist, some of which are based on this ASTM method. Many users of suchpackages specify that the seal have a minimum strength of 0.70 poundsper inch in a T-peel test. Accordingly, seal strengths that are at leastabout 0.70 pounds per inch are especially desirable. In someapplications, the seal strength desirably is not so great that one ormore of the package components will tear before the seal opens. Adesirable seal strength in such applications is thus greater than 0.70pounds per inch but lower than a value that would result in tearing ofone or more of the package components upon opening.

[0006] The base component in this type of package should be imperviousto bacteria and other pathogens. Typical materials used in making basecomponents include, but are not limited to, such polymers as nylon,polyester, polypropylene, polyethylene and polystyrene. Of thesematerials, nylon, polyester, polyethylene (including but not limited tolow density, linear low density, ultra low density and high densitypolyethylene), and polypropylene are particularly useful for flexiblebase components. Polyester, polyethylene (including but not limited tohigh density polyethylene), polypropylene, and polystyrene are examplesof polymers that are particularly useful for rigid containers such astubs or trays. Those skilled in the art will recognize that thepreceding lists of base components and materials used in making basecomponents are for illustration purposes only and are not meant to beexclusive.

[0007] The breathable cover is typically a nonwoven web, which is asheet comprised of cellulose fibers, synthetic fibers, or a combinationthereof. Different materials, including some fabrics, have been used toform breathable covers for use in medical supply packaging. (As usedherein, the term “fabric” is intended to encompass any sheet-like or webmaterial that is formed in whole or in part from a plurality of fibers).One such material comprises webs of polyolefin fibers such as thespunbonded polyolefin material sold under the trademark TYVEK® by E. I.Du Pont De Nemours & Co. Others are webs comprising cellulose fibers orpapers that have been saturated with one or more polymers such asacrylates to impart certain qualities to the paper. Such polymerreinforcement improves one or more of dimensional stability, resistanceto chemical and environmental degradation, resistance to tearing,embossability, resiliency, conformability, moisture vapor transmission,and abrasion resistance, among others. In addition, saturation ofpaper-based webs by such emulsions ties down the cellulose fibers sothat particulate generation is reduced when the fabric is torn orpeeled. Polymer saturated papers provide certain advantages overpolyolefin webs. Webs made from polyolefins often lack the suppleness,softness, and drapability that polymer saturated papers may possess. Useof cellulose webs is also a less expensive alternative to the polyolefinwebs.

[0008] The polymer is normally applied by a saturation process, whichinvolves dipping the formed fabric web into a bath of emulsion orsubjecting the fabric web to an emulsion-flooded nip. Alternatively, thewebs may be subjected to polymer impregnation while still on the fomlingwire through the use of various emulsion processes and the like. Polymerimpregnation may also occur prior to forming the web as described inInternational Publication Number WO 99/00549 to Deka, et. al. Processesin which polymer is applied to a formed web are generally referred toherein as “latex saturation” processes. The term “latex” as used hereinrefers to a synthetic polymer emulsion. Processes in which polymer isapplied to the fibers before the web is formed are generally referred toherein as “wet end deposition,” the term “wet end” referring to thesection of the paper machine.

[0009] Examples of latex-saturated substrates include productsdesignated as BP 336 and BP 321 that are available from Kimberly-ClarkCorporation. These products are base papers that may be used as medicalpackaging substrates and comprise various amounts of cellulosic pulpsand synthetic latex.

[0010] In addition to being permeable to sterilizing gases andrelatively impermeable to bacteria, the fibrous webs should be strongand should exhibit relatively high internal bonding, or delamination andtear resistance. Surgical instruments and trays containing varioussurgical instruments are often sterilized while wrapped in the medicalpackaging substrates. After sterilization, the storage containers maythen be placed on shelves in a storage facility for later transportationto the operating room. Because such storage and transportation mayinvolve the bumping or rubbing of the storage containers against oneanother, the medical packaging substrates must be strong enough towithstand such handling.

[0011] In addition, fibrous webs may also possess a certain degree offluid repellency to prevent further transmission of the bacteria. It isoften desired that medical packaging substrate be non-toxic, odorless,lint-free, drapable, supple, smooth, etc. The need for such “touch andfeel” characteristics depends on the particular product for which thebacteria barrier fabric is to be used.

[0012] Fibrous web packaging substrates may be formed from eithercellulosic fibers alone, synthetic polymeric fibers alone, or acombination of both cellulosic and synthetic fibers. For example, U.S.Pat. No. 5,204,165 to Schortmann discloses a nonwoven laminate havingbarrier properties that is described as being suitable for industrial,hospital, and other protective or covering uses. The laminate consistsof at least one thermoplastic fiber layer bonded with a wet-laid fabriclayer made from a uniform distribution of cellulose fibers, polymericfibers, and a binder. In one embodiment, spunbond polyester fiber layersare ultrasonically bonded on each side of a wet-laid barrier fabric madeof eucalyptus fibers and polyester fibers. The barrier fabric is bondedwith an acrylic latex binder. The binder is added to the formedpolymeric/cellulosic web after the web is formed. The binder may beadded by any one of several methods, including foamed emulsion, gravureroll polymer emulsion, spraying, padding and nip-pressure binderpick-up. Schortmann is an example of a barrier fabric formed using alatex saturation process.

[0013] Another process for saturating a formed web with a latex binderis disclosed in U.S. Patent No. 5,595,828 to Weber. A polymer-reinforcedpaper, which includes eucalyptus fibers, is disclosed. After forming theweb from eucalyptus fibers and, optionally, other fibers such asnon-eucalyptus cellulosic fibers and/or synthetic fibers, the web issaturated with a latex binder.

[0014] Various latex emulsions have been used as binder materials forpaper-based webs as well as coating materials for nonwoven webs.Polymeric emulsions of acrylates, polymethacrylates, poly(acrylic acid),poly(methacrylic acid), and copolymers of the various acrylate andmethacrylate esters and the free acids; styrene-butadiene copolymers;ethylene-vinyl acetate copolymers; nitrile rubbers oracrylonitrile-butadiene copolymers; poly(vinyl chloride); poly(vinylacetate); ethylene-acrylate copolymers; vinyl acetate-acrylatecopolymers; neoprene rubbers or trans-1,4-polychloroprenes;cis-1,4-polyisoprenes; butadiene rubbers or cis- andtrans-1,4-polybutadienes; and ethylene-propylene copolymers have beenused to saturate paper-based webs in order to enhance strength anddelamination resistance.

[0015] Latexes have also been used as barrier coatings to form fluidimpervious webs. For example, in U.S. Pat. Nos. 5,370,132 and 5,441,056to Weber et al. a nonwoven material's surface is first treated with arepellent coating material such as a fluorocarbon. The treated surfaceis then coated with a barrier coating which may be one of the variouslatex emulsions. Unlike a saturated web which will have latex particlesthroughout the web, the described webs in the Weber et al. patent have asurface barrier coating comprising a latex or other barrier material.

[0016] Although many latex-saturated webs perform well enough tofunction as medical packaging barrier substrates, saturating a cellulosepaper web with a polymer emulsion to obtain the necessary strengthtypically results in reduced barrier efficacy. It is possible to improvebarrier by refining the pulp as part of the papermaking process.Refining can be described as a grinding action that separates the pulpinto individual fibers and works to free the outer fibrils from thesurface of the fiber. This action creates more sites on the fiber forbonding with other fibers and thereby increases the tensile strength anddelamination resistance of the web. Refining also reduces the size ofopen passages through the sheet and thus decreases the porosity orpermeability of the sheet. Refinement techniques are well documented inthe art and the relationship between parameters of refinement processesand the desired characteristics of resulting webs is well known topersons skilled in the art. One disadvantage of using highly refinedwebs, however, is that refining tends to reduce the tear resistance of aweb. Despite the availability of several alternative bacteria barrierfabrics, a need still exists for further improved medical substratesthat can be used in forming bacteria barrier packages.

[0017] A disadvantage of using polymer saturated paper as the breathablecover is the absence in the art of a saturant that will confer upon thepaper the ability to form a strong adhesive bond with the basecomponents through heat sealing without compromising drapability of thepaper. Heat sealing refers broadly to any process involving the creationof an adhesive seal between two objects through the application of heat,often with pressure. In many applications the base component andbreathable cover are attached by heat sealing. Some base components arecomprised of polymers capable of forming bonds with other polymericmaterials by means of heat sealing. Other base components are extrudedor coated with an outer layer comprising heat sealable polymers.Examples of polymeric materials found in base components that have suchstrong sealability include, but are not limited to polypropylene,polyethylene, (including but not limited to low density, linear lowdensity, and ultra low density polyethylene), various copolymers ofvinyl acetate (including, but not limited to, low and high vinyl acetatecompositions of ethylene vinyl acetate) and ethylene acrylic acid.Because many polyolefin webs contain polymeric material that formsstrong heat seals with materials used in base components, such webs canbe heat sealed to base components, often eliminating the need forapplying an adhesive coating to the surface of the breathable cover. Bycontrast, many polymers used to saturate papers for use as breathablecovers lack sufficient affinity for heat sealing to materials used inbase components and thus cannot form as strong of a bond without the useof a temperature sensitive adhesive coating.

[0018] A saturated paper that can form a sufficiently strong bond to thebase component through heat sealing could in many cases eliminate theneed to coat the saturated paper altogether. Allowing the saturatedpaper to bond directly to the base component will result in a seal thatinvolves only one interface of different materials rather than twointerfaces on either side of the sealant. Eliminating one of theinterfaces reduces the potential for seal failure. In addition, removingthe coating step would reduce the potential for departures from productspecifications due to errors in that step of the process. Examples ofproduction errors associated with coating include “skip coating,” inwhich the coating is not applied to an entire surface, or the formationof pinholes in the coating. Eliminating the use of the coating and thecoating production step would also result in cost savings.

[0019] There have been some efforts to develop papers that can be sealedto base components containing heat sealable polymeric materials byimpregnating papers with heat sealable polymeric materials. For example,International Publication Number WO 98/24970 to Cohen et al. teachesimpregnating papers with a polymer emulsion primarily for the purpose ofimproving strength. Cohen et al. discusses heat sealability of theimpregnated papers and includes examples that involve impregnating paperwith ethylene acrylic acid and polyethylene, two heat sealable saturantmaterials.

[0020] In practice, however, saturating paper with heat sealablepolymeric materials has resulted in webs that have less than desirabledrapability for packages containing some medical products. “Drapability”refers essentially to flexibility and absence of stiffness in a fibrousweb. Sufficient drapability allows a web to conform to the contours ofthe products contained in the package and thus to assure a higher degreeof contact between the web and the surface area of the product. Asofter, more drapable web is less brittle and more flexible and wouldtherefore provide for easier handling of flexible packages with lesspotential for puncture or tear. Coatings applied to saturated papers inthe past have served not only to promote heat sealing but also toenhance the paper's function as a barrier to pathogen contamination.Even for a saturant that forms stronger bonds when heat sealed, theremay be a need for a temperature sensitive adhesive coating that iscompatible with the saturant for use in some applications in which it isdesirable to increase the seal strength further, to improve barrierproperties, or both. What is needed in the art therefore is a saturantthat may be used to confer heat sealability on a paper withoutcompromising the drapability of saturated paper. A paper saturated withsuch a saturant could be sealed without the need for an adhesive coatingand would have utility for medical products and other products for whichdrapable heat sealable packaging is desired. In the event that a need touse the paper along with a coating is found to exist, there will be afurther need in the art for a coating that is compatible with thesaturated paper.

[0021] What is further needed in the art are substrates that readilyallow sterilization materials to enter into the package and sterilizethe enclosed appliances while at the same time exhibiting sufficientstrength, at least in terms of delamination and tear resistance, tofunction as medical packaging. In particular, a need exists formaintaining the barrier efficacy of latex-saturated webs withouthindering the enhanced strength of these webs resulting fromlatex-saturation without additional refinement. Any webs that allow forsufficient amounts of latex add-on without decreasing barrier efficacywould be improvements over known latex-saturated substrates used asmedical packaging.

SUMMARY OF THE INVENTION

[0022] The present invention is directed to a saturant for fibrous webs,or papers, that can be used to confer upon a fibrous web an increasedseal strength when heat sealed to a base component, as compared to otheracrylic polymer saturants, while still allowing the web to retain itsdrapability as well is its porosity to sterilization gases and abilityto function as a barrier to pathogens characteristic of papers saturatedwith acrylic polymer emulsions. The saturant combines a heat sealablepolymeric material with other saturant polymeric materials that are notheat sealable but that improve the drapability of the saturated paper.

[0023] The present invention is further directed to a fibrous web thatis saturated with the saturant of the present invention and a method forsaturating the fibrous web with the saturant. The present invention isfurther directed to packaging using the saturated fibrous web and amethod of manufacturing the packaging.

[0024] While the saturant of the present invention eliminates the needto apply a coating to fibrous webs in many applications, the inventionfurther relates to a coating containing heat sealable polymericmaterials that can be used with the saturated paper of the presentinvention, if desired to enhance further the paper's seal strength orits function as a barrier to bacteria and other pathogens. Accordingly,the present invention is further directed to a temperature sensitiveadhesive coating that can be used with the saturated fibrous web of thepresent invention.

[0025] The present invention is also directed to saturated papers thatovercome some of the shortcomings of the prior art by providing asufficiently strong latex-saturated paper-based web that also exhibitsadequate bacteria barrier efficacy to be used for improved medicalpackaging applications. The use of a particular type of latex as thesaturant provides the effective range of bacteria filtration while atthe same time allowing the web to maintain its enhanced strength anddelamination resistance that are required when such substrates areemployed to wrap surgical trays, surgical instruments, medicalappliances and the like prior to sterilization.

[0026] This aspect of the invention consists of a paper-containingmedical packaging substrate that has been saturated with a latex havinga glass transition temperature of −20° C. or less. Examples of suchlatex emulsions are certain acrylic latexes sold under the trade nameHYSTRETCH® by Noveon, Inc. Cleveland, Ohio. In particular, three knownacrylic latex saturants that meet these characteristics are HYSTRETCH®V-29, HYSTRETCH® V-43, and HYSTRETCH® V-60. The “V-29”, “V-43”, and“V-60” designations represent the glass transition temperatures of theparticular latexes. Thus, HYSTRETCH® V-29 has a glass transitiontemperature of −29° C.; HYSTRETCH® V43 has a glass transitiontemperature of −43° C.; and HYSTRETCH® V-60 has a glass transitiontemperature of −60° C. and are examples of the latexes that provide therequired attributes of the present invention.

[0027] These and other features and advantages of the present inventionwill become apparent after a review of the following detaileddescription of the disclosed embodiments and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Definitions

[0029] The following definitions apply throughout this application.

[0030] The term “acrylate,” “acrylic polymer” and. “acrylic latex,” asdescribed herein, each refer to homopolymers and heteropolymers ofacrylate esters and methacrylate esters.

[0031] The term “base component material” is defined broadly to includeany chemical or substance contained in a base component of a packagethat is capable of forming heat seals with one or more polymers.Examples include, but are not limited to polypropylene, polyethylene,(including but not limited to low density, linear low density, and ultralow density polyethylene.), various copolymers of vinyl acetate(including, but not limited to, low and high vinyl acetate compositionsof ethylene vinyl acetate) and ethylene acrylic acid.

[0032] The term “seal strength” when used in connection with a fibrousweb saturated with a given saturant shall refer to the strength of aseal between a fibrous web and a base component as determined by aT-peel test using ASTM method F904-98 with the following changes: samplewidth is 15 mm, jaw travel is 125 millimeters at a rate of 300millimeters per minute.

[0033] The term “enhanced seal strength,” when used in connection with asaturant that comprises both a drapable saturant component and anadditional saturant polymer, refers to the fact that the saturantconfers a seal strength upon a seal between a fibrous web saturated withthe saturant and a specific base component comprising a specific basecomponent material that is higher than the seal strength of a seal madeunder identical sealing conditions between an identical base componentand a fibrous web saturated under identical saturating conditions andhaving an identical composition except that it comprises the drapablesaturant component without the additional saturant polymer. The term“significantly enhanced seal strength,” when used in connection with asaturant that comprises both a drapable saturant component and anadditional saturant polymer, refers to the fact that the saturantconfers a seal strength upon a seal between a fibrous web saturated withthe saturant and a specific base component comprising a specific basecomponent material that is at least about twice as strong as the sealstrength of a seal made under identical sealing conditions between anidentical base component and a fibrous web saturated under identicalconditions and having an identical composition except that it comprisesthe drapable saturant component without the additional saturant polymer.

[0034] The term “degree of enhanced seal strength,” when used inconnection with a saturant that comprises both a drapable saturantcomponent and an additional saturant polymer, refers to the amount bywhich the seal strength of a seal between a fibrous web saturated withthe saturant and a specific base component comprising a specific basecomponent material is higher than the seal strength of a seal made underidentical sealing conditions between an identical base component and afibrous web saturated under identical conditions and having an identicalcomposition except that the saturant comprises the drapable saturantcomponent without the additional saturant polymer.

[0035] The term “drapable saturant component” means a polymer that, whenapplied as a saturant to a fibrous web without other polymers, resultsin a web with a Gurley stiffness of less than about 165, expressed inmilligrams. Examples of saturant polymeric materials include, but arenot limited to, acrylic polymers, nitrile copolymers, and copolymers ofbutadiene and styrene. It has been found that polymers with glasstransition temperatures less than 10° C. generally provide for a moredrapable web than higher glass transition temperature polymers. Examplesof such acrylic polymers include HYCAR® 26083, 26703 (aformaldehyde-free version of HYCAR® 26083), 26469, and 26322 availablefrom Noveon, Inc., RHOPLEX® B-15J available from Rohm & Haas, andFLEXBOND® 274 from Air Products and Chemicals, Inc. Examples of nitrilecopolymers include TYLAC® 68513-00, available from Reichhold, and HYCAR®1562, available from Noveon, Inc. An example of a butadiene-styrenecopolymer is GOOD-RITE® SB1168 available from Noveon, Inc. The examplesprovided are not intended to be exhaustive. Persons of ordinary skill inthe art will recognize that embodiments including other polymers arepossible and the present invention is not limited to any particularpolymer or relative concentration. It was observed, however, that use ofa drapable saturant component with a glass transition temperature ofabout 10° C. or lower resulted in a saturated paper with improvedflexibility and drapability as compared to saturants with higher glasstransition temperatures. One desirable embodiment is the use of anacrylate such as RHOPLEX® B-15J with a glass transition temperature of−5° C. Still another desirable embodiment uses an acrylic polymer suchas HYCAR® 26703 or 26083 with a glass transition temperature of −15° C.

[0036] The term “Gurley stiffness” means stiffness determined by TAPPImethod T543om-00.

[0037] The term “Persoz hardness” or “Rocker hardness” means hardnessdetermined by Test Method B of American Society for Testing and Material(ASTM) Method No. D4366-95.

[0038] With respect to above definitions that relate to seal strengthand changes in seal strength, persons skilled in the art will alsorecognize that other factors besides the saturant composition affect theseal strength between a saturated fibrous web and a base component. Suchfactors include the type of base component material, the amount of basecomponent material present in the base component, and, if the basecomponent material is limited to a coating or outer layer on the basecomponent, the thickness of the coating or outer layer. In addition,conditions under which a heat seal was made can affect sealability,specifically sealing temperature, amount of pressure applied, andduration of exposure to heat and pressure. For purposes of thesedefinitions, however, it is assumed that all conditions regardingsaturant composition, base component material composition, and saturantand sealing conditions are unchanged, with the exception of the presenceor absence of the additional saturant polymer.

[0039] Heat-Sealable Saturated Fibrous Webs

[0040] The present invention is directed to a composition used as asaturant for fibrous webs, such as papers, that will confer enhancedseal strength upon the fibrous webs when sealed to base componentmaterials. The invention is further directed to saturants that willprovide fibrous webs with a seal strength of at least about 0.70 lb/in.The invention is further directed to the saturated papers and a methodfor saturating them. The invention is further directed to packaging thatincludes the saturated papers and a method for making the package.Finally, the invention is directed to a temperature sensitive adhesivecoating that can be used with the saturated papers.

[0041] Saturant Compositions

[0042] The composition of this aspect of the present invention includesa blend of at least two polymeric materials. One of the polymers is aheat sealable polymeric material that will confer upon the paper theability to be heat sealed to a base component that contains heatsealable polymeric material. Examples of heat sealable polymericmaterials that may be used in the saturant of the present inventioninclude, but are not limited to, homopolymers and heteropolymers oflower alkenes. The term “lower alkenes” means ethylenes and/orpropylenes. Examples of heat sealable polymers include but are notlimited to polyethylene, polypropylene, ethylene acrylic acid andethylene vinyl acetate. Desirable heat sealable saturant polymersinclude polyethylene and ethylene acrylic acid. An especially desirableheat sealable polymer is ethylene acrylic acid. An example ofcommercially available ethylene acrylic acid is MICHEM® Prime 4983R,available from Michelman, Inc. MICHEM® Prime 4983R is a dispersion ofDow PRIMACOR® 59801, a copolymer of ethylene and acrylic acid that hasan ethylene content of approximately 80%. An example of a commerciallyavailable polyethylene is MICROTHENE® F FN501-11; a dispersible powderavailable from Equistar Chemicals L.P.

[0043] The other polymer in the saturant is the drapable saturantcomponent. This component helps assure the softness, drapability, andflexibility of the saturated sheet. In one desirable embodiment thedrapability, as measured by Gurley stiffness, is less than about 165milligrams in the machine direction. In another desirable embodiment thedrapability, as measured by Gurley stiffness, is less than about 155milligrams in the machine direction. In another desirable embodiment thedrapability, as measured by Gurley stiffness, is less than about 145milligrams measured in the machine direction. In another desirableembodiment the drapability, as measured by Gurley stiffness, is lessthan about 100 milligrams measured in the cross direction. In anotherdesirable embodiment the drapability, as measured by Gurley stiffness,is less than about 95 milligrams measured in the cross direction. Inanother desirable embodiment the drapability, as measured by Persozhardness, is less than about 70 seconds (mean value). In anotherdesirable embodiment the drapability, as measured by Persoz hardness, isless than about 65 seconds (mean value). In another desirable embodimentthe drapability, as measured by Persoz hardness, is less than about 55seconds (mean value).

[0044] The saturant provides fibrous webs with enhanced seal strength.In one desirable embodiment, the webs exhibit a significantly enhancedseal strength. In another desirable embodiment, the degree of enhancedseal strength is at least a ten-fold increase. In another desirableembodiment, the degree of enhanced seal strength is at least atwenty-fold increase. In another desirable embodiment, the seal strengthis 0.70 lb/in. or greater but lower than a value that would result intearing of one or more of the package components upon opening; that is,lower than the internal bond strength of either the reinforced web orthe base component. Saturants that provide fibrous webs with sealstrengths of at least about 0.70 lb/in are also within the presentinvention, regardless of whether such saturants involve an “enhancedseal strength” or a “significantly enhanced seal strength” as comparedto another saturant.

[0045] Saturant compositions may also include additives that provide thesaturant or the saturated web with desirable qualities. By way ofexample and not an exclusive list, antifoaming agents, chemicals for pHadjustment, pigments, processing aids, and dispersing agents are amongthe possible additives. Examples of antifoaming agents include, but arenot limited to, products such as NALCO® 7518 available from NalcoChemical Company or DOW CORNING®Antifoam available from Dow CorningCorporation. Chemicals used to adjust pH include, but are not limitedto, ammonia, sodium hydroxide, potassium hydroxide, hydrochloric acid,acetic acid, and sulfuric acid. Dispersing agents or surfactantsinclude, but are not limited to, products such as TAMOL® 731A availablefrom Rohm & Haas Co., PLURONIC® F108 available from BASF Corporation,SMA® 1440 Resin available from ATOFINA Chemicals, Inc., and TERGITOL®15S available from Union Carbide Corp. Examples of processing aids mayinclude, but are not limited to, products such as NOPCOTE® DC-100Aavailable from Geo. Specialty Chemicals, Inc. SCRIPSET® 540 availablefrom Solutia, Inc. and AQUAPEL® 752 available from HerculesIncorporated. Examples of pigments used to increase opacity include butare not limited to, titanium dioxide such as TI-PURE® Rutile TitaniumDioxide available from E. I. Du Pont De Nemours & Co. and kaolinpigments, which are available from a variety of manufacturers. A widerange of pigments and dyes may also be added to impart color to thesaturated sheet. The foregoing list of categories of additives andexamples of categories is provided by way of example and is not intendedto be exhaustive. Embodiments including other additives are possible andthe present invention is not limited to any particular set of additivesor relative concentrations.

[0046] Persons skilled in the art will recognize that the amount of eachcomponent used in the composition may vary depending on factors such asthe desired use of the composition and the components to be used in thecomposition, among others. For example, the composition of processingaids, chemicals for pH adjustment, and dispersing agents may be variedto improve process conditions during production. Adjusting pH, forexample, can assist in controlling viscosity of the saturant. Dispersingagents may be used, for example, to improve the dispersion of a pigmentin the saturant. Additionally, product specifications such as opacityand wet strength may dictate the composition of the saturant.

[0047] Saturated Fibrous Webs

[0048] Since the invention is also directed toward saturated papers, thepaper or fibrous web to be used is also a component of the invention.Such webs are generally prepared by any of a variety of well knownmethods for air laying or wet laying fibers to form the web. The fibersmay include cellulose fibers alone or in combination with syntheticfibers.

[0049] Sources of cellulose fibers include, by way of example and not byway of limitation, woods, such as softwoods and hardwoods; straws andgrasses, such as rice, esparto, wheat, rye, and sabai; canes and reeds,such as bagasse; bamboos; woody stalks, such as jute, flax, kenaf, andcannabis; bast, such as linen and ramie; leaves, such as abaca andsisal; and seeds, such as cotton and cotton linters. Softwoods andhardwoods are the more commonly used sources of cellulose fibers; thefibers may be obtained by any of the commonly used pulping processes,such as mechanical, chemimechanical, semichemical, and chemicalprocesses. Examples of softwoods include, by way of illustration only,longleaf pine, shortleaf pine, loblolly pine, slash pine, Southern pine,black spruce, white spruce, jack pine, balsam fir, douglas fir, westernhemlock, redwood, and red cedar. Examples of hardwoods include, again byway of illustration only, aspen, birch, beech, oak, maple, eucalyptus,and gum. Softwood and hardwood Kraft pulps generally are desirable fortoughness and tear strength, but other pulps, such as recycled fibers,sulfite pulp, and the like may be used, depending upon the application.Cellulose fibers may also be bleached to whiten the pulp fibers usingvarious chemical processes.

[0050] Different cellulose fibers provide different attributes to thefinished web. The choice of fiber sources is dependent on the finalapplication of the web. For example, softwood fibers are often includedin a web to increase tensile strength. Hardwood fibers may be selectedfor their ability to improve formation, a term referring to theuniformity in distribution of the fibers. In one desirable embodiment,the paper contains between about 30% and about 75% eucalyptus fibersbased on total dry weight of the fibers. In another desirableembodiment, the paper contains between about 50% and about 75%eucalyptus fibers based on total fiber dry weight. Other fibers in thoseembodiments include northern softwood fibers, either alone or incombination with synthetic fibers.

[0051] In accordance with this aspect of the present invention, any ofthe various wood and nonwood pulps and other cellulosic fibers may beincorporated into the pulp furnish. Illustrative examples of suitablelignocellulosic pulps include southern pines, northern softwood pulps,red cedar, hemlock, black spruce and mixtures thereof. Examples ofhigh-average fiber length wood pulps include those available under thetrade designations LL19 available from Kimberly-Clark Corporation andINTERNATIONAL PINE® available from International Paper Company. Othervarious cellulosic fibers that may be used in the present inventioninclude eucalyptus fibers, such as Primacell Eucalyptus, available fromKlabin Riocell, and other hardwood pulp fibers available under the tradedesignations LL16 available from Kimberly-Clark Corporation, St. Croixhardwood available from Georgia-Pacific Corporation, and Leaf Riverhardwood available from Georgia-Pacific Corporation. Other cellulosicfibers may be utilized in the present invention, depending on theparticular characteristics desired.

[0052] Refinement of the pulp may be conducted in order to improve theproperties necessary to use the web as a bacteria barrier. Inparticular, refinement of the pulp may be carried out by beating orotherwise agitating the cellulosic material until the material issufficiently separated into relatively individual pulp fibers. Suchrefinement may be carried out by any number of various known methodssuch as in commercial grade pulp refiners. Such refining processes arewithin the known skill in the art and often improve the bacteriafiltration efficiencies of webs made from highly refined pulp.

[0053] The pulp of the invention may be a mixture of different typesand/or qualities of pulp fibers. For example, the invention may includea pulp containing more than about 50 percent by weight, low-averagefiber length pulp and less than about 50 percent by weight, high-averagefiber length pulp (e.g., virgin softwood pulp). The low-average fiberlength pulp may be characterized as having an average fiber length ofless than about 1.2 mm. For example, the low-average fiber length pulpmay have a fiber length of from about 0.7 mm to about 1.2 mm. Thehigh-average fiber length pulp may be characterized as having an averagefiber length of greater than about 1.5 mm. For example, the high-averagefiber length pulp may have an average fiber length of from about 1.5 mmto about 6 mm. The fiber mixture may contain about 75 percent, byweight, low-average fiber length pulp and about 25 percent, by weight,high-average fiber length pulp.

[0054] The low-average fiber length pulp may be certain grades of virginhardwood pulp and secondary (i.e., recycled) fiber pulp from sourcessuch as, for example, newsprint, reclaimed paperboard, and office waste.The high-average fiber length pulp may be bleached and/or unbleachedvirgin softwood pulps.

[0055] Types of synthetic fibers commonly used include, by way ofexample and not by way of limitation, polymers comprised of rayon,polyvinyl alcohol, alcohol copolymers, polyesters, polyamides,polyolefins, copolymers, and blends thereof. Examples of polyestersinclude, but are not limited to, polyethylene terephthalate,polybutylene terephthalate, polytetramethylene terephthalate,polycyclohexylene-1,4-dimethylene terephthalate, and isophthalatecopolymers thereof. Examples of polyamides include, but are not limitedto, nylon 6, nylon 6/6, nylon 4/6, nylon 11, nylon 12, nylon 6/10, andnylon 12/12. Examples of polyolefins include, but are not limited to,polyethylenes (including but not limited to high density polyethylene,medium density polyethylene, low density polyethylene, ultra low densitypolyethylene, linear low density polyethylene and others),polypropylenes (including but not limited to isotactic polypropylene,atactic polypropylene, syndiotactic polypropylene, blends of theforegoing, and others), polybutylenes, (including but not limited topoly(1-butene), and poly(2-butene), polypentenes, including but notlimited to poly(1-pentene), poly(2-pentene), poly(3-methyl-1-pentene);and poly(4-methyl-1-pentene)) and copolymers and blends thereof.Suitable copolymers include random and block copolymers prepared fromtwo or more different unsaturated olefin monomers, such asethylene/propylene and ethylene/butylene copolymers. Of these suitablepolymers, more desirable polymers are polyolefins, most desirablypolyethylene and polypropylene, because of their commercialavailability, as well as their chemical and mechanical properties. Thoseskilled in the art will recognize that the preceding list is notexclusive and that blends or copolymers of different polymers may beused. In addition, fibers that combine different polymer fibers in amulticomponent configuration may also be considered for use as asynthetic fiber. One example of a multicomponent fiber is comprised oftwo fibers having differing characteristics combined into a singlefiber, commonly called a bicomponent fiber. Bicomponent fibers generallyhave a core and sheath structure where the core polymer has a highermelting point than the sheath polymer. Other bicomponent fiberstructures, however, may also be utilized. For example, bicomponentfibers may be formed with the two components residing in variousside-by-side relationships as well as concentric and eccentric core andsheath configurations. One particular example of a suitable bicomponentfiber is sold under the name CELBOND® T255 by KoSa. CELBOND® T255 is asynthetic polyester/polyethylene bicomponent fiber that is capable ofadhering to cellulosic fibers when its outer sheath is melted at atemperature of approximately 128° C.

[0056] The purpose of including synthetic fibers in papers is to imparttear resistance to the sheets. Adding synthetic fibers, however, canalso reduce the web's resistance to delamination. Including syntheticfibers in a cellulose based sheet also increases the permeability of thesheet and thereby reduces its Gurley porosity value. Gurley porosityvalues are determined using TAPPI Test Method No. T 460 om-96 (1996).Persons skilled in the art will appreciate that these considerationsmust be weighed when determining synthetic fiber content of a web. Forpurposes of medical packaging applications, it has been observed thatsynthetic fiber content over about 30% (based on total dry fiber weight)results in significant loss of strength and ability to control porosity.In one desirable embodiment, synthetic fiber content is between zero andabout 10% (based on total dry fiber weight).

[0057] Persons skilled in the art are also familiar with severaladditives that are incorporated into webs during the papermakingprocess. Examples of such additives include, but are not limited to, wetstrength agents, chemicals for pH adjustment, slimicides, sizing agents,drainage aids, defoamers, corrosion inhibitors, fillers, and syntheticpolymers. Such additives may be used in different combinations and indifferent amounts depending upon the process and equipment used to formthe sheet. The use of papermaking additives and their purposes are wellknown and documented in the art.

[0058] The refinement of cellulose fibers prior to forming the sheetwill impact the final properties of the web. It has been observed that ahighly refined sheet that has a Gurley porosity for one ply of betweenabout 20 seconds/100 cc and 120 seconds/100 cc (measured aftersaturation), and that has a basis weight of about 85 g/m², providesdesirable pathogen barrier characteristics and has desirablepermeability to sterilization gases when used in this aspect of thepresent invention.

[0059] Method of Saturating Fibrous Webs

[0060] Another element of the invention is the method of saturating thewebs. Several methods of impregnating or saturating paper are well knownto persons skilled in the art. By way of example and not limitation,saturation methods that are well known include brushing, flooded nipsaturation, doctor blading, spraying, and direct and offset gravurecoating. The present invention is not limited to any particularapplication process, and persons skilled in the art will recognize thatalternative embodiments are possible with these and other saturationtechnologies. The amount of saturant or polymer blend applied to thesheet is commonly referred to as percent pickup or add-on. Percentpickup is calculated, on a dry weight basis, by dividing the dry weightof saturant applied by the dry weight of the sheet before saturation andmultiplying the result by 100. It has been observed that optimal sealingand barrier properties are achieved for the present invention whenpickup values are greater than about 25%. One desirable embodiment usesa pickup value of between about 35% and about 40%. Another desirableembodiment uses a pickup value of between about 40% and about 45%. Stillanother desirable embodiment uses a pickup value of between about 45%and about 50%. Persons skilled in the art are familiar with methods fordesigning saturation processes and controlling parameters to achieve aspecific pickup value for a given paper.

[0061] Embodiments also exist in which the polymer is added to thefibers before the web is formed. This saturation step is performedthrough addition of the polymer to the “wet end” of a web formingprocess and is commonly referred to as “wet end deposition” or “latexdeposition.” The term “wet end” refers to the portions of the webforming process prior to water removal from the fiber mixture; the term“latex” refers to the polymer emulsion. By way of example only, the wetend may refer to any mixing, holding, or refining areas of the process.Alternatively, the wet end may include the forming section just prior towater removal. Examples of wet end deposition may be found inInternational Publication No. 99/00549 to Kapik et. al., which teachesthe use of wet end deposition for improving the strength of a medicalpackaging paper while maintaining a porous substrate; U.S. Pat. No.5,466,336 to Kinsley. Jr., which describes a process for coagulating anaqueous polymer into a fiber slurry for the manufacture of a paper-basedproduct.

[0062] After saturation, the web may be dried by any method orcombination of methods known in the industry. Drying methods include butare not limited to, application of heat to the web by use of convectionovens, radiant heat, infrared radiation, forced air ovens, heated rollsor cans, or other heat sources. Another example of a drying method isallowing the web to air dry without the addition of thermal energy otherthan that present in the ambient environment.

[0063] Packages Comprising Fibrous Webs

[0064] The packages that include the saturated web and the method formaking the packages are two additional elements of the invention. Thepackaging will include the saturated web of the present invention andthe other component, which is the base component. The base component andsaturated web are assembled and sealed using a heat seal device thatapplies heat to the edges or surfaces of the web and base component inwhich a seal is desired. Persons skilled in the art will recognize thatother components may be incorporated in the package. Examples include,without limitation, internal packaging for protection and separation ofcomponents, and labels attached to the package. The amount and type ofadditional components varies widely and depends on the product packagedand its intended use.

[0065] Adhesive Coatings

[0066] The adhesive coating that may be used with the saturated paper isalso an element of the invention. The adhesive coating can be used inapplications where the saturation of the web alone does not provide thedesired seal strengths with the selected film. The coating can also beused to decrease the web permeability and thereby increase the bacteriabarrier. The coating is comprised of between about 50% and about 85%ethylene vinyl acetate and between about 15% and about 50% ethyleneacrylic acid, with both percentages based on the total dry weight of thecoating. The relative concentrations of these two compounds will beadjusted to maximize compatibility with the sealant used in the basecomponent. One desirable embodiment uses an ethylene acrylic acid levelbetween about 20 and about 30%, expressed as dry weight. Anotherdesirable embodiment uses an ethylene acrylic acid level of betweenabout 15% and about 20%, expressed as dry weight.

[0067] The coating composition may also include additives that provide acoating or coated paper with desirable qualities. Examples include, butare not limited to, crosslinking agents, chemicals for pH adjustment,and surfactants. XAMA® 7, available from Sybron Chemicals is an exampleof one crosslinking agent. To adjust pH, acids such as hydrochloricacid, sulfuric acid, acetic acid, and oxalic acid, and bases such asammonia, sodium hydroxide, and potassium hydroxide may be added.Examples of surfactants or dispersing agents include, but are notlimited to, TAMOL® 731A available from Rohm & Haas Co., TRITON® X100available from Union Carbide Corp. and PLURONIC® F104 available fromBASF Corporation. Where crosslinking agents are used, they typically areincluded at levels between about 0.5% and 2.0% (based on the total dryweight of the coating), although other ranges are possible. Levels of pHadjusting compounds typically range up to about 1.0% of the total dryweight of the coating depending on the amount of pH adjustmentnecessary. Surfactant levels typically range between about 0.5% andabout 2.0% of the total dry weight of the coating, although other rangesare possible. Embodiments including coatings with different additives ordifferent quantities of the additives are possible and the presentinvention is not limited to any particular additive, blend of additives,or relative concentrations.

[0068] Several technologies for applying coatings are known in the artincluding, by way of example and not limitation, rod coating, dipcoating, spray coating, gravure coating, knife coating, and slotcoating. Persons skilled in the art will recognize that alternativeembodiments are possible with these and other coating technologies andthe present invention is not limited to any particular applicationprocess.

[0069] After coating, the web may be dried by any method or combinationof methods known in the industry. Drying methods include but are notlimited to, application of heat to the web by use of convection ovens,radiant heat, infrared radiation, forced air ovens, heated rolls orcans, or other heat sources. Another example of a drying method isallowing the web to air dry without the addition of thermal energy otherthan that present in the ambient environment. It is desirable that theweb be dried in a manner that prevents contact of the coated side with aheated surface such as the surface of a heated can. It has been observedthat direct contact of the coated side to a heated surface may result inpartial removal of the coating, an effect sometimes referred to aspicking.

[0070] The porosity of the finished sheet is greatly affected by theamount and type of coating applied since heavier coatings will cause thepaper or fabric to be less permeable to sterilization gases. Heaviercoatings will also increase adhesive properties and seal strengths. Fora medical packaging substrate it is generally desirable to have a Gurleyporosity below about 120 sec/100 cc. Gurley porosity is an indicator ofpermeability; a higher Gurley porosity value indicates that a sheet haslower permeability to sterilization gases and to pathogens. Sheets withGurley porosities greater than 120 sec/100 cc may make sterilizationdifficult due to insufficient permeability to sterilization gases.However, decreasing the Gurley porosity of the sheet also increases thelikelihood of penetration by bacteria or other pathogens unless apolymer that improves bacteria barrier is applied, although the minimumGurley porosity varies depending on composition of the paper andsaturant. Furthermore, some coating processes are less capable ofapplying an effective coat with a low coat weight than others. Selectinga coat weight for a sheet is thus a balance between the capabilities ofthe coating apparatus used, permeability and porosity to both pathogensand sterilization gases, and the desired seal strength. As examples,coat weights between 3.75 g/m² and 11.00 g/m² add-on, on a dry weightbasis, have been found to provide the desirable porosity range with websthat have Gurley porosity values below 20 sec/100 cc prior to coating.In embodiments that use dispersed ethylene vinyl acetate powder, personsskilled in the art can use milling of the ethylene vinyl acetate powderto control particle size and thereby control the permeability of thecoating to obtain a desired permeability. Larger particle sizes, forexample, result in greater permeability.

[0071] Thus, the invention relates to a coating that can be used withthe saturated webs of the present invention. In one embodiment, thecoating comprises a copolymer of ethylene and acrylic acid monomers anda copolymer of ethylene and vinyl acetate monomers. The inventionfurther relates to a fibrous web coated with the coatings of the presentinvention.

[0072] Saturants that Improve Barrier Efficacy

[0073] In another aspect, the present invention is a medical packagingmaterial comprising a cellulose-containing substrate web that has beensaturated with a latex having a glass transition temperature of −20° C.or less. More specifically, the present invention involves thesaturation of the webs with such low-glass transition temperaturelatexes in order to improve the barrier efficacy of the web.

[0074] Conventional latex saturants, when employed at the add-on levelsrequired to obtain the necessary increased strength characteristics,tend to reduce the barrier efficacy of medical packaging substrate webs.It is believed that the efficacy is reduced because the number oftortuous pathways, which entrap microorganisms within the web, arereduced by polymer saturation. The particular latexes having glasstransition temperatures of −20° C. and below have been found to actuallyimprove the percent bacterial filtration efficiency (“% BFE”) and logreduction value (“LRV”), both common industry determinations of barrierefficacy, of latex-saturated paper as compared to latex-saturated papersthat have not utilized these particular latexes.

[0075] For example, the latex-saturated webs of this aspect of thepresent invention will generally exhibit higher % BFEs and LRVs thancomparable latex-saturated webs. Generally, the higher the estimatedLRV, the greater the bacteria barrier properties. For example, an LRVchange from 1 to 2 indicates a ten times improvement in the barrier.

[0076] The paper-based webs of this aspect of the present invention maybe formed from cellulosic pulp fibers alone, or a mixture of cellulosicpulp and synthetic fibers. The above discussion regarding suitablefibers for heat-sealable papers, as well as the discussion of refinementof such fibers, applies equally to this aspect of the invention.

[0077] In making the web of this aspect of the present invention, a pulpfurnish is formed according to normal paper-making or web-makingprocedures. Briefly, and by way of illustration only, the substrate maybe made by preparing an aqueous suspension of fibers with at least about50 percent, by dry weight, of the fibers being cellulosic fibers;distributing the suspension on a forming wire; removing water from thedistributed suspension to form a paper; and then treating the paper withthe saturant. In general, the aqueous suspension is prepared by methodswell known to those having ordinary skill in the art. Similarly, methodsof distributing the suspension on a forming wire and removing water fromthe distributed suspension to form a paper also are well known to thosehaving ordinary skill in the art.

[0078] In addition to noncellulosic fibers, the aqueous pulp-containingsuspension from which the substrates are made may contain othermaterials as is well known in the papermaking art. For example, thesuspension may contain acids and bases to control pH, such ashydrochloric acid, sulfuric acid, acetic acid, oxalic acid, phosphoricacid, phosphorous acid, sodium hydroxide, potassium hydroxide, ammoniumhydroxide or ammonia, sodium carbonate, sodium bicarbonate, sodiumdihydrogen phosphate, disodium hydrogen phosphate, and trisodiumphosphate; alum; sizing agents, such as rosin and wax; dry strengthadhesives, such as natural and chemically modified starches and gums;cellulose derivatives such as carboxymethyl cellulose, methyl cellulose,and hemicellulose; synthetic polymers, such as phenolics, latexes,polyamines, and polyacrylamides; wet strength resins, such asurea-formaldehyde resins, melamine-formaldehyde resins, and polyamides;fillers, such as clay, talc, and titanium dioxide; coloring materials,such as dyes and pigments; retention aids; fiber deflocculants; soapsand surfactants; defoamers; drainage aids; optical brighteners; pitchcontrol chemicals; slimicides; and specialty chemicals, such ascorrosion inhibitors, and flame-proofing agents.

[0079] In addition to the use of the particular polymers disclosedherein, other binder materials may be used in forming the webs of thisaspect of the invention. For example, the additional binder materialsmay be used as an additional constituent of the saturant in conjunctionwith the polymers having the specific glass transition temperatures setforth herein. On the other hand, such binder materials may be used atvarious points in the web-forming or web-saturating process to addadditional strength or filtration characteristics to the web.

[0080] Any of the latex binders commonly employed for reinforcing papercan be utilized and are well known to those having ordinary skill in theart. Suitable binders include, by way of illustration only,polyacrylates, including polymethacrylates, poly(acrylic acid),poly(methacrylic acid), and copolymers of the various acrylate andmethacrylate esters and the free acids; styrene-butadiene copolymers;ethylene-vinyl acetate copolymers; nitrile rubbers oracrylonitrile-butadiene copolymers; poly(vinyl chloride); poly(vinylacetate); ethylene-acrylate copolymers; vinyl acetate-acrylatecopolymers; neoprene rubbers or trans-1,4-polychloroprenes;cis-1,4-polyisoprenes; butadiene rubbers or cis- andtrans-1,4-polybutadienes; and ethylene-propylene copolymers.

[0081] Specific examples of commercially available latex binders are setforth as examples in Table 1 below: TABLE 1 Polymer Type ProductIdentification Polyacrylates HYCAR ® 26083, 26084, 26120, 26104, 26106,26322, 26410, 26469 Noveon, Inc. Cleveland, Ohio Rhoplex ® HA-8, HA-12,HA-16 NW-1715, B-15 Rohm and Haas Company Philadelphia, PennsylvaniaCarboset ® XL-52 Noveon, Inc. Cleveland, Ohio Styrene-butadienecopolymers Butofan ® 4264, 4262 BASF Corporation Charlotte, NorthCarolina DL 219NA, DL 239NA Dow Chemical Company Midland, MichiganNitrile rubbers HYCAR ® 1572, 1577, 1570X55, 1562X28 Noveon, Inc.Cleveland, Ohio Poly(vinyl chloride) Vycar ® 352, 552 Noveon, Inc.Cleveland, Ohio Ethylene-acrylate copolymers Michem ® Prime 4990R, 4983RMichelman, Inc. Cincinnati, Ohio Adcote ® 56220 Rohm & Haas CompanyPhiladelphia, Pennsylvania Vinyl acetate-acrylate Xlink ® 2833copolymers Vinamul ™ Polymers Bridgewater, New Jersey

[0082] Various other additives may also be used in forming the bacteriabarrier substrate. For example, sizing agents to impart waterresistance, wet-strength agents to improve delamination resistance, andother agents may be added either to the furnish or to the formed web.One such exemplary sizing agent is AQUAPEL® 752 available from HerculesIncorporated of Wilmington, Del., and one such exemplary wet-strengthagent is PAREZ® 631NC available from Cytec Industries, Inc. of WestPaterson. N.J. Other agents, include, by way of example only, starchesand dry-strength resins which also enhance the physical properties ofthe web by increasing the delamination resistance of the final product.One such exemplary starch is a cationic potato starch sold under thedesignation ASTRO® X-200 and one such exemplary dry-strength resin isACCOSTRENGTH® 85-PHP, also available from Cytec Industries. Anotherexemplary dry-strength resin is ACCOSTRENGTH® 85-3000, also availablefrom Cytec Industries. Cross-linking agents, such as X-LINK® 2833 fromVinamul Polymers and XAMA®7 available from Sybron Chemicals, Inc. ofBirmingham, N.J., and/or hydrating agents may also be added to the pulpfurnish or to the formed web.

[0083] After the web is formed, the web will then be saturated with thepolymer emulsion having a glass transition temperature of −20° C. orbelow. As used herein, the term “saturant” is synonymous with the term“binder” and is meant to include any polymeric material which may beused to bind the fibers of the fibrous web or nonwoven substratetogether. The saturant may be applied as either a solution of a polymerin a suitable solvent or as a dispersion of very small polymer particlesin a liquid phase, such as water, e.g., as a latex. For example, thesaturant may be any of the latex binders commonly employed forreinforcing papers, provided such latex has a glass transitiontemperature of −20° C. or less. In particular, the acrylic latexes,which are polyacrylates, meeting this glass transition temperaturethreshold are particularly useful as the saturants for such medicalpackaging fabrics. In addition, saturant blends comprising more than onelatex binder may be employed. In these blended saturant formulations,one or more of the latexes may have a glass transition temperature ofgreater than −20° C., provided that one or more latexes with glasstransition temperatures of −20° C. or less comprise at least 50% of thesaturant by dry weight.

[0084] Various latex binders are well known to those having ordinaryskill in the art and include, by way of illustration only,polyacrylates, including polymethacrylates, poly(acrylic acid),poly(methacrylic acid), and copolymers of the various acrylate andmethacrylate esters and the free acids; styrene-butadiene copolymers andcarboxylated versions thereof; ethylene-vinyl acetate copolymers;nitrile rubbers or acrylonitrile-butadiene copolymers; poly(vinylchloride); poly(vinyl acetate); ethylene-acrylate copolymers; vinylacetate-acrylate copolymers; neoprene rubbers ortrans-1,4-polychloroprenes; cis-1,4-polyisoprenes; butadiene rubbers orcis- and trans-1,4-polybutadienes; and ethylene-propylene copolymers.

[0085] In particular, the acrylic latexes such as the above describedpolyacrylates tend to provide the desired features of the presentinvention. While other binder systems may provide adequate strength inthe latex-saturated webs, the polyacrylate saturants exhibit the mostdesirable bacterial filtration efficiencies.

[0086] The saturation of a fabric is well known in the art and a fabricmay be saturated, for example, by spraying the saturant solution ontoone or both sides of the web. Saturation of the fabric may also beaccomplished by dipping the web into a bath of saturant and removing theexcess liquid by passing the web through a nip roller arrangement. Othersaturating methods include brushing and doctor blading and the presentinvention is not limited to any particular saturating process.

[0087] If desired, the paper may be dried after the web is formed andprior to treatment of the paper with the saturant. Drying of the papermay be accomplished by any known means. Examples of known drying meansinclude, by way of illustration only, convection ovens, radiant heat,infrared radiation, forced air ovens, and heated rolls or cans. Dryingalso includes air drying without the addition of thermal energy, otherthan that present in the ambient environment.

[0088] In one particular method of saturating the web, the web isexposed to an excess of saturant and then squeezed so as to control theamount of material added on to the web. The squeezing of excess saturantfrom the web may be accomplished by passing the web between rollers. Inthe process, excess, squeezed-out, saturant may be returned to thesupply for further use.

[0089] After squeezing out excess material to control the saturantadd-on, the saturated web may then be dried. Drying may be achieved bypassing the fabric around a series of steam heated drums at atemperature appropriate for the particular saturant composition beingused. Alternatively, the web material impregnated with saturant can beair-dried.

[0090] The web of this aspect of the invention will typically besaturated at an add-on level of from about 10 to about 100 percent,based on the dry weight of the fibrous web. For example, the saturantmay be present in the saturated paper at a level of from about 20 toabout 70 percent. As another example, the saturant may be present in thesaturated paper at a level of from about 30 to about 60 percent.

[0091] Saturant total solids in the saturant composition may range from10 to 60 weight percent, depending on the desired dry saturant pickup.Dry pickup ranges from 10 to 80 dry parts of saturant per 100 dry partsof fibrous web material by weight. Particularly satisfactory ranges ofdry pickup are from 20 to 70 dry parts of saturant per 100 dry parts offibrous web, and saturant total solids in a range of 20 to 50 weightpercent in the saturant composition are used. In other embodiments, thedry pickup may be from about 30 to about 50 dry parts, or from about 40to about 50 dry parts, of saturant per 100 dry parts of fiber in theweb. Wet saturant pickup can range from about 40 to about 300 wet partsper 100 parts of fibrous web material by weight.

[0092] The expressions “by dry weight,” “dry parts,” and “based on thedry weight” refer to weights of fibers, e.g., cellulosic fibers, orother materials which are essentially free of water in accordance withstandard practice in the papermaking art. When used, such expressionsmean that weights were calculated as though no water were present.

[0093] A particularly effective saturant may include from about 60 toabout 100 percent, on a dry weight basis, of a latex reinforcing polymer(or a blend of latex reinforcing polymers) having a glass transitiontemperature of −20° C. or less and from about 0 to about 40 percentfiller or pigment. Additionally, crosslinking agents, sizing agents,lubricants, antifoaming agents, and acids and bases may comprise about 0to about 15 percent of the saturant.

[0094] After formation of the polymer-impregnated substrate, the fabricis then supplied to a maker of medical packaging. The packaging makerthen transforms the fabric into the appropriate packaging necessary forstoring medical devices and appliances and surgical instrumentation.Such medical packaging may take the form of sterile wraps for encasingsurgical instrument trays, bags, pouches, or other sterilizablecontainers.

[0095] The present invention is further described by the examples thatfollow. Such examples, however, are not to be construed as limiting inany way either the spirit or scope of the present invention.

EXAMPLES

[0096] Embodiments with Improved Heat Sealability

[0097] Fibrous webs were saturated with the saturant of the presentinvention and the heat-sealability of those samples was compared withsamples saturated with known saturant polymers.

Example 1

[0098] A web saturated with the saturant of the present invention wasprepared. The web was formed using ECF bleached kraft eucalyptus pulpavailable from Votorantim Celulos e Papel SA and a bleached Northernsoftwood pulp prepared by Kimberly-Clark Corporation and sold under thebrand name Longlac 19 or LL19. LL19 pulp is composed of primarily blackspruce and jack pine and has a population average fiber length ofapproximately 1.0 mm and a length weighted average fiber length ofapproximately 2 mm as determined by TAPPI test method T 271 om-98. Thecomposition of the paper was 69% eucalyptus and 31% softwood based ontotal dry fiber weight. The pulp also contained PAREZ®607, a wetstrength additive manufactured by Cytec Industries, Inc., in an amountof 0.3% based on total dry fiber weight. The pulp was dispersed andrefined in an aqueous slurry. A web was then formed on a commercial finepaper machine using a standard Fourdriner table. The web was wet pressedand dried on a series of steam cans prior to saturation.

[0099] The web was saturated with a formula comprised of an acrylatepolymer and an ethylene acrylic acid emulsion. In the disclosedembodiment, MICHEM® Prime 4983R, a dispersion of ethylene acrylic acidavailable from Michelman, Inc., was combined with HYCAR® 26703, anemulsion of acrylic polymers available from Noveon, Inc. The ethyleneacrylic acid comprised approximately 45.5% of the saturant based on thetotal dry weight. The acrylate comprised approximately 37.2% of thesaturant based on the total dry weight. Other components included in thesaturant included TI-PURE® Rutile Titanium Dioxide available from E. I.Du Pont De Nemours & Co. (16.4% by dry weight); NALCO® 7518 antifoamingagent available from Nalco Chemical Company (0.1% by dry weight);NOPCOTE® DC-100A available from Geo Specialty Chemicals, Inc. (0.6% bydry weight); and TAMOL® 731A dispersing agent available from Rohm & HaasCo. (0.2% by dry weight). The desired level of saturant in the web wasthen achieved by diluting the saturant to between 28% and 32% solidswith water.

[0100] The saturant was applied to the dried web through flooded nipsaturation. The nip consisted of two rolls, one of which rotated througha pan containing the saturation formula. The saturant was applied to thesheet from the bottom roll, which carried the formulation from the panto the web and from a stream of saturant directed at the intersection ofthe two rolls and the sheet. The excess saturant was removed by nippressure and was returned to the supply. The water in the saturant wasremoved by drying the web on steam heated can dryers, leaving the solidsof the formula in the web. With respect to polymer pickup, saturant wasadded to the paper in an amount between 33% and 40% of the dry weight ofthe fibers. The web was then calendered in a steel calender prior totesting. The final basis weight of the sample was approximately 98 g/m².

Comparative Example 2

[0101] A web was prepared and saturated using the procedures of EXAMPLE1 with the exception of fiber selection and saturation formula contents.COMPARATIVE EXAMPLE 2 was prepared from 100% LL19 pulp, a bleachedNorthern softwood pulp. The web was formed, pressed, and dried in thesame process as EXAMPLE 1. The saturation formula for COMPARATIVEEXAMPLE 2 comprised approximately 79% of a saturant of acrylate polymersold as HYCAR® 26469 by Noveon, Inc. based on the total dry weight.Approximately 20% of the emulsion was TI-PURE® Rutile Titanium Dioxide;additives such as dispersing agents (0.1%), antifoam agents (0.01%), andprocess aids (0.89%) were also used. The desired level of saturant inthe web was then achieved by diluting the saturant to between 28% and32% solids with water. The dry add-on of the saturant was between 45%and 50% of the dry weight of the fibers. All percentages expressed abovewere in dry weight. The web was saturated and finished in a similarmanner to EXAMPLE 1. The final basis weight of COMPARATIVE EXAMPLE 2 wasapproximately 114 g/m².

Comparative Example 3

[0102] A web was prepared and saturated using the procedures of EXAMPLE1 with the exception of fiber selection, saturation formula contents,and method of saturation. COMPARATIVE EXAMPLE 3 was prepared with 78%LL19, a bleached Northern softwood pulp, and 22% LL16, a bleachedNorthern hardwood pulp. The web was formed, pressed, and dried in asimilar manner as EXAMPLE 1. However the web was saturated in alaboratory on a bench scale. The saturation formula used for COMPARATIVEEXAMPLE 3 comprised approximately 83% acrylate polymer sold as HYCAR®26769, an emulsion containing acrylic polymers available from Noveon,Inc. and approximately 17% TI-PURE® Rutile Titanium Dioxide as anadditive for color. A dispersing agent was present in less than 0.1%.All percentages expressed above were in dry weight. The total solids ofthe formula were reduced to approximately 35% with water.

[0103] With respect to polymer pickup, saturant was added to the paperin an amount equal to approximately 46% of the dry weight of the fibers.The rate of polymer add-on was adjusted by controlling nip pressurethrough adjustments to the force on the top roll and through dilution ofthe saturation formula discussed above. The force was adjusted by movingan eight pound weight along each of the two lever arms supported by thetop roll. After saturation, the wet sheet was dried on a steam heatedcan dryer. The final basis weight of COMPARATIVE EXAMPLE 3 wasapproximately 85 g/m².

Comparative Example 4

[0104] A web was prepared and saturated using the procedures ofCOMPARATIVE EXAMPLE 3 with the exception of saturation formula contents.COMPARATIVE EXAMPLE 4 was saturated with a formula comprisingapproximately 83% ethylene vinyl chloride polymer sold as AIRFLEX® 4530and approximately 17% TI-PURE® Rutile Titanium Dioxide. A dispersingagent was present in less than 0.1%. All percentages expressed abovewere in dry weight. The total solids of the formula were reduced tobetween 28% and 35% with water. The dry polymer add-on was approximately44%. The final basis weight of COMPARATIVE EXAMPLE 4 was 84 g/m².

Comparative Example 5

[0105] A web was prepared and saturated using the procedures ofCOMPARATIVE EXAMPLE 3 with the exception of saturation formula contents.COMPARATIVE EXAMPLE 5 was saturated with a formula comprisingapproximately 83% by weight of a vinyl acetate homopolymer sold asVINAC® XX-211 and approximately 17% TI-PURE® Rutile Titanium Dioxide. Adispersing agent was present in less than 0.1%. The total solids of theformula were reduced to between 30% and 35% with water. All percentagesexpressed above were in dry weight. The dry polymer add-on wasapproximately 40%. The final basis weight of COMPARATIVE EXAMPLE 5 was82 g/m².

Comparative Example 6

[0106] A web was prepared using the procedures of EXAMPLE 1 with theexception of fiber selection, saturation formula contents, and method ofsaturation. COMPARATIVE EXAMPLE 6 was prepared with 69% VCP Eucalyptus,a bleached Eucalyptus pulp, and 31% LL19, a bleached Northern softwoodpulp. The web was formed, pressed, and dried in a laboratory on a benchscale. The web was then saturated using the procedures in COMPARATIVEEXAMPLE 3 with the exception of saturant formula contents and add-on.The saturation formula used for COMPARATIVE EXAMPLE 6 comprisedapproximately 83% acrylate polymer sold as HYCAR® 26703 andapproximately 17% TI-PURE® Rutile Titanium Dioxide. A dispersing agentwas present in less than 0.1%. All percentages expressed above were indry weight. The total solids of the formula were reduced toapproximately 30% with water. The dry polymer add-on was approximately42%. The final basis weight of COMPARATIVE EXAMPLE 6 was approximately99 g/m².

[0107] The sealing properties of the saturated webs of EXAMPLE 1 andCOMPARATIVE EXAMPLES 2-6 were evaluated by sealing the webs to variousflexible base components, referred to herein as “films.” Each filmcontained a base component material, as that term is defined herein. Theseals were generated using a Model # 12AS laboratory heat sealermanufactured by Sentinel Packaging Industries of Hyannisport, Mass. Theheat sealer is equipped with two platens, or jaws, measuring 1″ wide by12″ long. The top jaw was heated and could be applied to the bottom jawunder pressure. Portions of each saturated web that were approximately4″ long and 2″ wide were sealed to portions of films that wereapproximately 4″ long and 1.25″ wide. The films used each had most oftheir base component materials distributed on only one face (side) ofthe films. Accordingly, the films would be expected to seal on only oneside, so they were placed between two layers of the saturated web(paper) such that a layer of paper was in contact with each side of thefilm and each platen. A seal temperature of 350° F. was used for sealingwith a pressure of 55 psi. The time the films and webs were heldtogether in the jaw, or dwell time, ranged between about 1.7 and about3.5 seconds dwell time depending on the time required to activate thefilm sealant at 350° F. During sealing, the film adhered to the layer ofpaper placed on the base component material side. The other layer ofpaper was removed and discarded. Each sealed sample, comprising onelayer of paper and one layer of film, was allowed to condition overnightat 22-24° C. and 48-52% relative humidity prior to testing.

[0108] The seal strength was tested by measuring the force required toseparate the two layers in a T-peel test. All T-peel tests in thisapplication were performed using ASTM method F904-98 with the followingchanges: sample width was 15 mm, jaw travel was 125 mm at a rate of 300millimeters per minute. The separation was started manually to a lengthof approximately 141 . Once separated, the sealed sample was cut down to15 mm width, retaining the original length. The film layer was placed inthe upper jaw of a constant rate of elongation tester, an INSTRON® 5500Ravailable from Instron Corporation. The paper layer was placed in thelower jaw with a 1″ separation between the two jaws. The lower jawremained stationary while the upper jaw moved vertically atapproximately 300 millimeters per minute. The upper jaw moved 125millimeters before the test was completed. During the test, the freeportion of the sample was manually supported at 90° from the jaws. Theforce required to continue the separation, or peel, was averaged for theduration of the test to result in the seal strength per 15 mm width. Thevalue generated from the test was in grams force/15 mm. The values wereconverted to pounds force/inch, a more common unit of measure in thepackaging industry.

[0109] As used in Table 2, “Sealing Temperature” refers to thetemperature of the heated platen, expressed in degrees Fahrenheit.“Sealing Pressure” refers to the pressure applied to the seal, expressedin pounds per square inch. “Dwell Time” refers to the duration of timein the seal, expressed in seconds.

[0110] Different samples were prepared by sealing each type of saturatedweb to each type of film. The same conditions were used for each sampleinvolving the same film type (e.g., all samples generated using PliantX3-451-819.0 as a film were generated with the same sealing conditions).The sealing conditions used can be seen in Table 2. The sealingconditions developed were those that were found to be optimal withEXAMPLE 1. Optimal conditions were those in which a seal formed that wasas strong as possible without exceeding the strength of the internalbond of the paper. Exceeding the internal bond of the paper results inthe paper delaminating and a tear occurring between layers of paperrather than in the seal. TABLE 2 Conditions for Seal Strength TestingSealing Temperature Sealing Dwell Time Film (° F.) Pressure (psi) (sec)Pliant X3-451-819.0 350 55 3.5 Pliant X5-539-169.3 350 55 1.7 RJR PD6260350 55 2.1 Winpak WH2021-55 350 55 1.7 CA20088C

[0111] Seal strength results, in lb/inch, for each sample with the abovefilms at the above conditions can be found in Table 3. Seal strengthrefers to the force required to separate the film from the sample usinga T-peel test pursuant to the ASTM method. TABLE 3 Seal strengths forExample 1 and Comparative Examples 2-6 (lb/inch) Comparative ComparativeComparative Comparative Comparative Film EXAMPLE 1 EXAMPLE 2 EXAMPLE 3EXAMPLE 4 EXAMPLE 5 EXAMPLE 6 Pliant X3- 0.717 0.094 not tested nottested not tested 0.096 451-819.0 Pliant X5- 1.022 0.033 0.068 0.0600.050 0.037 539-169.3 RJR 0.825 0.053 0.029 0.029 0.132 0.044 PD6260Winpak 0.646 0.012 not tested not tested not tested 0.029 WH2021- 55CA20088C

[0112] EXAMPLES 7-11 were prepared using a paper with the same fibercomposition as used in COMPARATIVE EXAMPLE 3. The paper was prepared andsaturated using the procedures of COMPARATIVE EXAMPLE 3, with theexception of saturation formula content. Various combinations of anacrylic polymer (HYCAR® 26703) and an ethylene acrylic acid polymer(MICHEM Prime® 4983R) were used. COMPARATIVE EXAMPLE 7 contained 100%ethylene acrylic acid polymer based on total dry weight of the combinedpolymers. EXAMPLE 8 contained 75% acrylic polymer and 25% ethyleneacrylic acid based on total dry weight of the combined polymers. EXAMPLE9 contained 50% acrylic polymer and 50% ethylene acrylic acid based ontotal dry weight of the polymers. EXAMPLE 10 contained 25% acrylicpolymer and 75% ethylene acrylic acid based on total dry weight of thepolymers. COMPARATIVE EXAMPLE 11 contained 100% acrylic polymer based ontotal dry weight of the polymers.

[0113] Seals were made with the films and under the conditions set forthin Table 2. Seal strength was determined using the same procedures andfor the same films as the tests performed for EXAMPLE 1. Seal strengthresults, in lb/inch, for each sample with the above films at the aboveconditions can be found in Table 4. TABLE 4 Seal strengths for Examples8-10 and Comparative Examples 7 and 11 (lb/inch) COMPARATIVE COMPARATIVEEXAMPLE EXAMPLE Film EXAMPLE 7 EXAMPLE 8 EXAMPLE 9 10 11 PliantX3-451-819.0 0.705 0.960 0.827 0.681 0.327* Pliant X5-539-169.3 0.8710.953 1.173 0.626 0.032 RJR PD6260 0.641 0.743 0.556 0.380 0.033 WinpakWH2021- 0.734 0.664 0.589 0.480 0.044 55 CA20088C

[0114] Although the 100% EAA in COMPARATIVE EXAMPLE 7 showed a lowerseal strength for all films than the 75% EAA/25% acrylic polymer inEXAMPLE 8, this is believed to be because pickup levels of saturant werelower. The preferred pickup level is greater than 25% and more desirablygreater than 30%. Increasing the pickup improves strength propertiessuch as internal bond, but also ensures that sufficient polymer isapplied to the web surface and fiber network to achieve adequateadhesion to the base component material. Specifically, pickup levelswere 24.5% for COMPARATIVE

Example 7. 30.7% for EXAMPLE 8, 41.1% for EXAMPLE 9, 42.7% for EXAMPLE10, and 39.4% for EXAMPLE 11.

[0115] Drapability of the Webs Saturated with the Invention

[0116] Drapability was compared using two different methods. First, thePersoz or Rocker hardness test was used to evaluate the samples. Testsused Test Method B of American Society for Testing and Material (ASTM)Method No. D4366-95, except that samples were conditioned for four hoursrather than 16 hours. Equipment was a Persoz pendulum on a rockerhardness tester manufactured by Thomas Scientific located in Swedesboro,N.J. (serial number 5976870). Average (mean) values were determinedbased upon measurements for ten samples. Results are presented in Table5. Values are expressed in seconds as specified in the method. TABLE 5Mean hardness Example (seconds) COMPARATIVE EXAMPLE 7 74 EXAMPLE 8 67EXAMPLE 9 64 EXAMPLE 10 54 COMPARATIVE EXAMPLE 11 (not tested)

[0117] Gurley stiffness was also determined for EXAMPLES 7-11 usingTAPPI Method No. T543om-00 in the machine direction (MD) and crossdirection (CD), using a 2.0″ wide×2.5″ long sample and the 5 g weight inthe 2″position. Equipment used was a Gurley Stiffness Tester from GurleyPrecision Instruments located in Troy, N.Y. (model number 4171-D andserial number 956341). The Gurley stiffness values (expressed inmilligrams) for each of the samples can be seen in TABLE 6. TABLE 6Gurley Stiffness, Gurley Stiffness, MD (mg) CD (mg) COMPARATIVE 169.7100.6 EXAMPLE 7 EXAMPLE 8 143.9 102.1 EXAMPLE 9 144.3 99.1 EXAMPLE 10143.9 93.5 COMPARATIVE 117.7 75.7 EXAMPLE 11

Example 12

[0118] Saturated webs are prepared according to the procedures ofEXAMPLE 1 except that a different saturant blend is used. Saturants areprepared as follows. An aqueous dispersion with 30% total dry solids isprepared that contains 99% by dry weight MICROTHENE® F FN501-11, a fineparticle polyethylene powder, and 1% by dry weight TRITON® X-100. Thesolution is milled using a Tri-Homo™ Colloid Mill, model number 2.5serial number 1739, sold by Sonic Corporation of Stratford, Conn. Thesolution is cycled through the colloid mill multiple times, each time ata lower gap setting, beginning at approximately 15 and ending at 3 or 4.After two to three cycles at the final gap setting, the solution iscollected from the colloid mill. Once milled, the dispersion is mixedwith an emulsion of an acrylate polymer in a variety of relative amountsto prepare saturants. One set of saturants is prepared in which theMICROTHENE® dispersion is mixed with HYCAR® 26083 available from Noveon,Inc. Another group of saturants is prepared by mixing the MICROTHENE®dispersion with RHOPLEX®B-15 from Rohm & Haas. Mixes with each acrylateemulsion are prepared in the percentages below in Table 7. Allpercentages are based on total dry weight of the component. Whereadditives are used, the additives include: processing aids (for example,NOPCOTE® DC-100A to prevent buildup on converting slitters) in amountsup to 1%, dispersing aids (for example, TRITON®X-100 or TAMOL® 731A toavoid separation of saturant components) in amounts up to 2%, fillers(for example TI-PURE® Rutile Titanium Dioxide or kaolin clay to increaseopacity) in amounts up to 8%, and chemicals for pH adjustment (forexample ammonia), where necessary to obtain a final saturant pH in thedesirable range between 7.5 and 8.5. All percentages are based on dryweight. TABLE 7 % Polyethylene % Acrylate dispersion emulsion %Additives (by weight) (by weight) (by weight) 60 40 0 55 40 5 55 45 0 5040 10 50 45 5 50 50 0 45 45 10 45 50 5 40 50 10

[0119] The saturant is then applied to a paper using the procedures setforth in. EXAMPLE 1 and is otherwise processed as set forth in EXAMPLE1.

[0120] Increasing Seal Strength Through Coating

Example 13

[0121] A web was prepared in a similar fashion to EXAMPLE 1 with theexception of fiber selection and saturation formula contents. EXAMPLE 13was prepared from 78.4% LL19 pulp, a bleached Northern softwood pulp and21.6% LL16 pulp. The web was formed, pressed, and dried in the sameprocess as EXAMPLE 1. The saturation formula for EXAMPLE 13 comprisedapproximately 41.4% ethylene acrylic acid and 41.4% acrylate polymerbased on the total dry weight. Approximately 16.5% of the saturant wasTi-Pure® Rutile Titanium Dioxide; additives included dispersing agents(0.09% TAMOL® 731A), antifoam agents, (0.01% NALCO® 7518), and processaids, (0.6% NOPCOTE® DC-100A). All percentages expressed above werebased on dry weight. The desired level of saturant in the web was thenachieved by diluting the saturant to between 28% and 35% solids withwater. The dry add-on of the saturant was between 42% and 48% of the dryweight of the fibers.

[0122] The web was saturated and finished in a similar manner toEXAMPLE 1. After finishing, the web was coated with a formula comprising78.2% MICROTHENE® F FE532, an ethylene vinyl acetate powder availablefrom Equistar Chemicals L. P. and 19.5% MICHEM® Prime 4983R an ethyleneacrylic acid emulsion. Additives were XAMA® 7 available from SybronChemicals, a crosslinking agent (1.2%), ammonia for pH adjustment(0.3%), and TRITON® X100, a dispersing agent Union Carbide Corp. (0.8%).The formula solids were adjusted to between 30% and 34% with water. Allpercentages expressed above were based on dry weight. The coating wasapplied to the web with a transfer roll which rotated in a pan ofcoating formula. Excess coating formula was metered off using a wiretightly wound around a steel rod (commonly known as a Meyer rod). A #18Meyer rod was used. The coat weight was approximately 9 g/m2. The finalbasis weight was approximately 93 g/m2. After coating, the sheet wasdried in an oven at between 120 and 170° C. until the sheet wasdetermined to be dry.

[0123] Seals were made with the films and under the conditions set forthin Table 2. Seal strength was determined using the same procedures andfor the same films as the tests performed for EXAMPLE 1. Seal strengthresults, in lb/inch, for each sample with the above films at the aboveconditions can be found in Table 8. The results demonstrate that thecoating significantly increases the seal strength. TABLE 8 Sealstrengths for Example 13 (lb/inch) Film EXAMPLE 13 Pliant X3-451-819.0** Pliant X5-539-169.3 2.013 RJR PD6260 1.512 Winpak WH2021-55 ** CA20088C

[0124] Enhancement of Bacteria Filtration Efficiency

[0125] The Examples were performed in order to demonstrate the bacteriafiltration efficiency enhancement in fibrous structures. Various paperswere saturated with latex compositions having various glass transitiontemperatures. The particular latexes were added-on at a rate of fromabout 30 to about 50 dry parts per 100 dry parts fiber in each case.Table 9 below indicates, with respect to each Example, the basis weightof the paper, a description of the paper composition and saturatingemulsion composition, the glass transition temperature of the saturant,the Gurley Porosity (which indicates the porosity or permeability of thesheet), the Bacteria Filtration Efficiency (% BFE) and the Log ReductionValue (“LRV”) (for some of the samples only).

[0126] Each of the samples was prepared by blending and refining theindicated amounts of cellulosic fibers in an aqueous slurry.Noncellulosic fibers, if used, were added to the slurry after refining.The fiber slurries were then deposited on a forming fabric or wire andthe water was removed. The resulting formed web was dried prior totreatment by polymer emulsion. The polymer emulsion was applied in eachcase by exposing the web to an excess of saturant in a flooded nip. Theexcess material was removed in the nip. The saturated sheet was thendried and steel-calendered at about 150 pounds per linear inch (“PLI”)prior to testing.

[0127] The porosity of the saturated sheets was determined according tothe Gurley Hill Porosity test pursuant to TAPPI Test Method T460om-96.The basis weight was determined by TAPPI Test Method T410om-98 and isreported in grams per square meter.

[0128] The Bacterial Filtration Efficiency (“BFE”) of the saturatedsubstrates was determined by employing a ratio of the bacterialchallenge counts to sample effluent counts, which yields the percentbacterial filtration efficiency (“% BFE”). The BFE test described belowwas performed by Nelson Laboratories (Salt Lake City, Utah). A cultureof Staphylococcus aureus was diluted in 1.5% peptone water to a preciseconcentration to yield challenge level counts of 2200±500 colony formingunits (“CFU”) per test sample. The bacterial culture suspension waspumped through a nebulizer at a controlled flow rate and fixed airpressure. The constant challenge delivery, at a fixed air pressure,formed aerosol droplets with a mean particle size (“MPS”) ofapproximately 3.0 microns. The aerosol droplets were generated in aglass aerosol chamber and drawn through a six-stage, viable particle,Andersen sampler for collection. The collection flow rate through thetest sample and Andersen sampler was maintained at 28.3 LPM (1 CFM).Test controls and test samples were challenged for a two-minuteinterval.

[0129] The delivery rate of the challenge also produced a consistentchallenge level of 2200±500 CFU on the test control plates. A testcontrol (no filter medium in the airstream) and reference material areincluded after 7-10 test samples. The Andersen sampler, a sieve sampler,impinged the aerosol droplets onto six agar plates based on the size ofeach droplet. The agar medium used was soybean casein digest agar(SCDA). The agar plates were incubated at 37° C. ±2° C. for 48 hours ±4hours, with shaking, and the colonies formed by each bacteria-ladenaerosol were droplet counted and converted to probable hit values usingthe hole conversion chart provided by Andersen. These converted countswere used to determine the average challenge level delivered to the testsamples. The distribution ratio of colonies for each of the six agarplates were used to calculate the MPS of the challenge aerosol.

[0130] The filtration efficiencies were calculated as a percentdifference between test sample runs and the control average using thefollowing equation: ${\frac{C - T}{C} \times 100} = {\% \quad {BFE}}$

[0131] Where: C=Average of control values; and T=Count total for testmaterial.

[0132] The measurement, % BFE, has an upper limit of 100%, indicating100% of the microorganisms were intercepted by the test material.

[0133] Bacteria Spore Penetration is measured according to ASTM F1608-95. According to this test method, a sheet sample is exposed to anaerosol of Bacillus subtilis var. niger spores for 15 minutes at a flowrate through the sample of 2.8 liters/minute. Spores passing through thesample are collected on a media and are cultured and the number ofcolony-forming units (“CFU”) is measured. The log reduction value(“LRV”) expresses the difference, measured in log scale, between thenumber of CFU on the control media and the number of CFU on the mediathat was behind the sample. This ability to resist passage ofmicroorganisms is calculated according to the following equation:

LRV=log₁₀ N ₀−log₁₀ N ₁

[0134] Where:

[0135] N₀=average bacterial challenge determined from the challengecontrol filter, CFU; and

[0136] N₁=average number of bacteria passing through Test Sample 1, CFU.If N₁<1, then LRV is expressed as>log₁₀N₀.

[0137] For example, an LRV of 5 represents a difference of 100,000cluster forming units. The range of measurable LRV is 0 to 5, where agreater number indicates the likelihood of greater barrier efficacy (asmeasured by this test). Ethox Corporation performed the LRVdeterminations. TABLE 9 Glass Basis Transition Gurley Weight TemperaturePorosity % EXAMPLE (g/m²) Description of Paper Fibers and SaturantComposition (° C.) (sec/100 cc) BFE LRV 14 84.6 High porosity basecomprised of 78.4% Northern (“N.”) −5 6 81 1.3 softwood fiber, 21.6%hardwood fiber, saturated with RHOPLEX B-15 acrylic polymer 15 84.6 Highporosity base comprised of 78.4% N. softwood −29 9 93.1 fiber, 21.6%hardwood fiber, saturated with HYSTRETCH ® V-29 acrylic polymer 16 84.6High porosity base comprised of 78.4% N. softwood −43 7 96.2 1.7 fiber,21.6% hardwood fiber, saturated with HYSTRETCH ® V-43 acrylic polymer 17114 Low porosity base comprised of 56.5% N. softwood −5 20 97.7 fiber,43.5% eucalyptus fiber, saturated with RHOPLEX B-15 acrylic polymer 18114 Low porosity base comprised of 56.5% N. softwood −43 15 99.9 fiber,43.5% eucalyptus fiber, saturated with HYSTRETCH ® V-43 acrylic polymer19 73.3 High porosity base comprised of 60.3% eucalyptus −43 2 97.4fiber, 29.7% N. softwood fiber, 10% low densitypolyethylene/polypropylene (“LDPE/PP”) fiber, saturated with HYSTRETCH ®V-43 20 84.5 High porosity base comprised of 60.3% eucalyptus 8 8 88fiber, 29.7% N. softwood fiber, 10% LDPE/PP fiber, saturated with HYCAR26084 acrylic polymer 21 84.5 High porosity base comprised of 60.3%eucalyptus −11 8.6 90 fiber, 29.7% N. softwood fiber, 10% LDPE/PP fiber,saturated with HYCAR 26410 acrylic polymer 22 84.5 High porosity basecomprised of 60.3% eucalyptus −15 11.7 92.8 fiber, 29.7% N. softwoodfiber, 10% LDPE/PP fiber, saturated with HYCAR 26703 acrylic polymer 2384.5 High porosity base comprised of 60.3% eucalyptus −5 7.5 90.4 fiber,29.7% N. softwood fiber, 10% LDPE/PP fiber, saturated with RHOPLEX B15acrylic polymer 24 84.5 High porosity base comprised of 78.4% N.softwood −43 8 96.9 fiber, 21.6% hardwood fiber, saturated withHYSTRETCH ® V-43 acrylic polymer

[0138] As can be seen in Table 10, the acrylic polymers sold under the“HYSTRETCH®” tradename are particularly useful in forming the medicalpackaging substrate of the present invention. In particular, where theGurley Hill porosity is high (such as 15 sec/100 cc), the use of aHYSTRETCH® acrylic polymer saturant having a glass transitiontemperature of −20° C. or less can result in a highly efficientbacterial filtration fabric.

[0139] The various HYSTRETCH® polymers employed in the Examples abovehave the following characteristics indicated in Table 7: TABLE 10 GlassTotal Transition Solids Viscosity Temperature Specific Acrylic Polymer(%) pH (cP) (° C.) Gravity HYSTRETCH ® 50 8.0 40 −60 1.01 V-60HYSTRETCH ® 50 8.0 200 −43 1.03 V-43 HYSTRETCH ® 49 8.0 70 −29 1.04 V-29

[0140] These and other modifications and variations to the presentinvention may be practiced by those of ordinary skill in the art,without departing from the spirit and scope of the present invention,which is more particularly set forth in the appended claims. Inaddition, it should be understood that aspects of the variousembodiments may be interchanged both in whole or in part. Furthermore,those of ordinary skill in the art will appreciate that the foregoingdescription is by way of example only, and is not intended to limit theinvention so further described in such appended claims. Therefore, thespirit and scope of the appended claims should not be limited to thedescription of the preferred versions contained therein.

1-20. (Cancelled)
 21. A medical package comprising a base componentsealed to a fibrous web, the fibrous web being saturated with acomposition comprising a blend of a latex polymer having a glasstransition temperature of 10° C. or less and a heat-sealable polymercomprising a homopolymer or heteropolymer of a lower alkene, wherein thefibrous web has a Gurley stiffness of less than about 165 milligrams inthe machine direction and a seal strength of at least about 0.70 poundper inch.
 22. The medical package of claim 21, wherein the basecomponent is impervious to bacteria.
 23. The medical package of claim21, wherein the base component is formed from nylon, polyester,polypropylene, polyethylene, polystyrene, or combinations thereof. 24.The medical package of claim 21, wherein the base component includes afilm.
 25. The medical package of claim 21, wherein the Gurley stiffnessof the fibrous web is less than about 145 milligrams in the machinedirection.
 26. The medical package of claim 21, wherein the Gurleystiffness of the fibrous web is less than about 100 milligrams in thecross direction.
 27. The medical package of claim 21, wherein the latexpolymer is an acrylic polymer.
 28. The medical package of claim 21,wherein the heat-sealable polymer comprises polyethylene, polypropylene,ethylene acrylic acid, ethylene vinyl acetate, or combinations thereof.29. The medical package of claim 21, wherein the fibrous web includescellulosic fibers.
 30. The medical package of claim 21, wherein thepercent add-on of the composition is at least about 25%.
 31. The medicalpackage of claim 21, wherein the fibrous web has a Gurley porosity ofless than about 120 seconds per 100 cubic centimeters.
 32. A medicalpackage comprising a base component heat-sealed to a fibrous web, thefibrous web containing cellulosic fibers and being saturated with acomposition comprising a blend of an acrylic latex polymer and ahomopolymer or heteropolymer of a lower alkene, wherein the fibrous webhas a Gurley stiffness of less than about 145 milligrams in the machinedirection and a seal strength of at least about 0.70 pound per inch. 33.The medical package of claim 32, wherein the base component isimpervious to bacteria.
 34. The medical package of claim 32, wherein thebase component is formed from nylon, polyester, polypropylene,polyethylene, polystyrene, or combinations thereof.
 35. The medicalpackage of claim 32, wherein the Gurley stiffness of the fibrous web isless than about 100 milligrams in the cross direction.
 36. The medicalpackage of claim 32, wherein the acrylic latex polymer has a glasstransition temperature of about 10 C or lower.
 37. The medical packageof claim 32, wherein the heat-sealable polymer comprises polyethylene,polypropylene, ethylene acrylic acid, ethylene vinyl acetate, orcombinations thereof.
 38. The medical package of claim 32, wherein thepercent add-on of the composition is at least about 25%.
 39. The medicalpackage of claim 32, wherein the fibrous web has a Gurley porosity ofless than about 120 seconds per 100 cubic centimeters.
 40. A medicalpackage comprising a base component heat-sealed to a fibrous web, thefibrous web containing cellulosic fibers and being saturated with acomposition comprising a blend of an acrylic latex polymer and aheat-sealable polymer selected from the group consisting ofpolyethylene, polypropylene, ethylene acrylic acid, ethylene vinylacetate, and combinations thereof, the percent add-on of the compositionbeing at least about 25%, wherein the fibrous web has a Gurley stiffnessless than about 165 milligrams in the machine direction, a Gurleyporosity of less than about 120 seconds per 100 cubic centimeters, and aseal strength of at least about 0.70 pound per inch.